The present invention relates to a soft tire which enables travel on soft ground, such as a sward of a golf course or the like, without forming ruts, a manufacturing process of the soft tire and a vehicle having such soft tires.
Various self propelled vehicles traverse soft surfaces, such as golf carts, golf course maintenance vehicles, sweepers such as for removing dust and debris, soil fillers, sand fillers, lawn mowers, aerators, and the like. In conventional self-propelled vehicles with high tread pressure of the tire, ruts can be formed due to sinking of the tire upon traveling on the soft ground surface. Such ruts can interfere with the use of the surface, such as playing golf in the ruts. Therefore, for example, golf carts are required to travel on a path apart from the sward. In case of the other self-propelling vehicles operating on the sward, the rear wheel is often formed into a single elongated roll form to stamp out the ruts formed by the front wheels. Also, the vehicle is driven steered reciprocally with small intervals for overlapping both sides of the rut formed by the rear wheel to remove the rut.
Thus, in the conventional golf course, it is inconvenient to drive the golf carts over the sward. Since a dedicated cart path is required, this represents an imposition on designing the golf course, or limiting the area available for the golf course. Other self propelled vehicles can be steered reciprocally on the sward for operation, mobility such as for changing direction, is low for the elongated single roll form rear wheel and this makes its efficiency quite low for various tasks.
There was described in Unexamined Japanese Patent Publication (Kokai) No. Heisei 8-58308 a soft tire having a flat surface, which is formed by fixing a particular hardness of thick cylindrical soft elastic body, such as a foamed polyurethane or the like, onto the outer peripheral surface of a wheel rim, and a vehicle with such soft tire. Upon traveling on a soft ground surface with this soft tire, such as the sward surface when weights of a vehicular body and of the occupants is loaded, the soft elastic tire body causes elastic deformation to widen the tread surface width, the tread pressure becomes low and this prevents sinking of the tire into the soft ground surface and thus avoids formation of a rut.
The soft tire of the above-identified publication provides a feature by which formation of a rut can be avoided. However, during the process of repeated actual traveling tests, it has been found that there is room to improve in the durability and mobility of the loaded vehicle. There is also a further opportunity to lower manufacturing costs.
During vehicle travel with the soft tires, elastic deformation of compression and expansion of the elastic tire body repeatedly occurs per each rotation of the tire. Furthermore, the rotational force of the driving wheels is transmitted to the ground surface by the elastic layer, and in the driven tires the wheels are rotated by a frictional resistance between the elastic tire body layer and the ground surface. In these cases, mutually opposite tensile forces act on the inner periphery and the outer periphery of the elastic tire body to cause elastic deformation in the peripheral direction constantly applying a force tending to peel off the contacting interface between the wheel and the elastic tire body layer. Therefore, the soft tire of the above-identified publication tends to lower the restoring ability from the deformed condition thus to easily cause peeling off at the contact interface to result in insufficient tire durability.
In the soft tire of the foregoing publication, in order to increase fixing strength of the contacting interface, a tire unit, in which collar portions are provided on both peripheral edges of the narrow wheel, is produced to combine a plurality of tire units on the wheel portion to form a wide soft tire. Therefore, assembly is quite cumbersome and increases the manufacturing costs. Since a wide tire width is required to reduce the tread pressure not to form a rut, mobility, such as changing of direction, etc., of the vehicle can become degraded.
It is an object of the present invention to eliminate the drawbacks of the prior art. Thus, it is an object of the present invention to provide a soft tire which can travel on the soft ground surface, such as a sward surface, without forming ruts, and can be produced easily and at low cost, with satisfactory durability, a manufacturing method therefor, and a vehicle adapted to travel on a soft ground surface, such as sward surface, with a lifting of the tire and requiring less maintenance.
Accordingly, the present invention is a soft tire assembly of a thick elastic layer of a foamed elastomer having an outer peripheral surface and cells in the foamed layer that are open to the exterior through the outer peripheral surface, or a mixture of cells open to the exterior and closed cells, wherein the expansion ratio of the foamed elastomer is from 1.5 to 6.0, and the elastomer has a specific gravity of from 0.5 to 2.0. The layer is mounted on a wheel rim, suitably of a metal, having an outer peripheral surface coated with a resin, and the foamed elastic layer is attached onto and about the outer peripheral surface of the wheel rim.
The soft tire assembly of the present invention is made by depositing a coating resin over the outer surface of a wheel rim, inserting the coated wheel rim into a casting and foaming mold, filling and foaming an expandable elastomer in a space within said mold between its inner peripheral surface and the outer surface of the wheel rim to form a thick elastic layer of foamed elastomer with a flat outer surface integrally with the wheel rim, the foamed layer having an expansion ratio of from 1.5 to 6, and removing an outer skin formed on at least the flat outer peripheral surface whereby foamed cells within said thick foamed elastic layer become exposed through the exterior through the outer peripheral surface of the layer.